Movable barrier operators of various kinds are known in the art. Such movable barrier operators often work in conjunction with a corresponding movable barrier such as a single panel or segmented garage door, a rolling shutter, a pivoting, swinging, or sliding gate or arm barrier, and so forth. In particular, the movable barrier operator typically responds to user inputs (often as input via a remotely located user interface) to effect selective movement of a corresponding movable barrier (for example, to transition the movable barrier back and forth between a closed and an opened position).
A variety of mechanisms may serve to effect the movement of a movable barrier, including electric motors linked to the movable barrier through chain, belt, or screw driven mechanisms. Fluid-based operators that rely upon a rigid cylinder are also known in the art as a way to effect the movement of a movable barrier. These systems rely upon either hydraulic or pneumatic pressure to actuate a piston mechanically linked to the movable barrier. When hydraulic or pneumatic pressure increases in the rigid cylinder, the piston extends from the cylinder. Fluid-based operators have not gained popular success, however. Expense of the system components, labor intensive installation, specialized knowledge or tools required for installation, and the large amount of space required for such systems have prevented their popular adoption. Rigid piston and cylinder mechanisms are expensive to manufacture, requiring tight tolerances and specialized materials. Fluid-based operators also rely upon complicated mechanisms to translate the motion of a rigid cylinder into motion of the movable barrier. In many cases, these mechanisms require large amounts of space and are difficult to install and calibrate. Some of the known fluid-based movable barrier operators rely upon a second rigid cylinder to counterbalance the weight of the door. This configuration increases the costs associated with the fluid-based operator, because it requires duplication of expensive piston and cylinder components.
In conjunction with vertically lifted movable barriers, for example single panel or segmented garage doors and rolling shutters, counterbalance mechanisms are typically provided to reduce the effort required to lift the movable barrier. Counterbalance mechanisms that rely upon mechanical springs, such as torsion or extension springs, are known in the art, as are pneumatic mechanisms that rely upon a rigid piston and cylinder acting as an energy storage device.
An example prior art counterbalance mechanism will be described with reference to FIG. 10, which illustrates a vertically lifted garage door 1001, installed using methods known in the art. The garage door 1001 has rollers 1010 that run along tracks 1020 at either side of the door. The tracks 1020 guide each segment 1002, 1003, 1004, and 1005 of the door 1001 as the door 1001 is raised or lowered. The tracks comprise a horizontal portion 1021 generally parallel to the ceiling of the garage and a vertical portion 1022 generally parallel to the door opening. The segments 1002, 1003, 1004, and 1005 are connected to one another by hinges 1009. A jackshaft 1030 (sometimes also referred to as a torsion bar) is mounted above the garage door 1001. Cables 1032 attach at either side of the bottom of the garage door 1001 and run vertically along the sides of the garage door 1001. The cables 1032 are spooled around drums 1040 at either end of the jackshaft 1030. The interaction of the cables and the drums cause the jackshaft to rotate as the garage door is raised or lowered. As the door 1001 lowers, the cables 1032 unspool from the drums 1040 and extend down with the door 1001. Similarly, as the door 1001 is lifted, the cables re-spool around the drums 1040. A torsion spring 1035 is coiled around the jackshaft 1030 and exerts a rotational force on the jackshaft 1030 such that the shaft 1030 has a tendency to re-spool the cables 1032. Through the cables 1032, the spring 1035 pulls against the weight of the door 1000, which makes it easier to raise the door 1000. In effect, the arrangement of the torsion spring 1035, jackshaft 1030, drums 1040, and cables 1032 reduce the weight of the door 1000.
A garage door opener 1050 lifts and lowers the garage door 1001 by pulling a carriage 1051 along a lift track 1052 using a chain, belt, or screw. The carriage 1051 is connected to the garage door 1001 through a linkage 1053. As the garage door is raised, the weight of the segments 1002, 1003, 1004, and 1005 becomes supported as they move from the vertical portion 1022 to the horizontal portion 1021 of the garage door track 1020. In this way, the force required to lift the garage door 1001 becomes less as more segments pass along the horizontal portion 1021 of the garage door track. The prior art torsion spring 1035 accommodates this decrease in the weight of the garage door 1000 because it exerts less force as it relaxes. The torsion spring 1035 must be sized appropriately so that the reduction in its force corresponds correctly to the position of the garage door. Any one of several sizes of torsion spring 1035 could be required, based on the width of the garage door 1001 and the relative weight of the garage door 1001. For example, different springs 1035 would be required for a two-car garage than for single car garages. Likewise, wood doors are substantially heavier than foam-cored metal doors and therefore require different springs 1035. Because this type of counterbalance mechanism is a commonly installed system, there is a need for counterbalance mechanisms that can be retrofitted on these types of existing movable barriers systems.
Counterbalance mechanisms that rely upon mechanical springs are known to have sudden failures that can be disturbing for people in the vicinity. If the spring is not adequately secured during installation, or if the spring loosens during ordinary operation, it may snap loose as the movable barrier is lowered. Further, mechanical springs typically have a relatively short lifespan. The mechanical springs known in the art and used to counterbalance the weight of movable barriers commonly fail after as few as 10,000 cycles. Particularly in industrial and commercial door installations, the limited lifespan of mechanical springs requires frequent replacement of the springs. Replacing these mechanical springs is a labor intensive procedure that requires disassembly of the entire jack-shaft assembly. The mechanical spring is coiled around the outside of the jackshaft, so the only way to replace the spring is to remove the jackshaft completely and slide the spring off the end of the shaft.
When used as counterbalance mechanisms, mechanical springs require careful selection to match the weight of the door. The characteristics of the spring, such as spring constant and/or the displacement the spring is capable of, must be selected according to the weight and size of the door. Because these characteristics are fixed in a mechanical spring, manufacturers must stock a variety of springs.
Pneumatic counterbalance mechanisms that rely upon a rigid piston and cylinder suffer from the high costs associated with fluid-based movable barrier operators. The system components are expensive to manufacture and install for many of the same reasons discussed above.
In light of these disadvantages of the known current counterbalance and movable barrier operator systems, there is a need for a counterbalance mechanism and movable barrier operator that is robust and capable of a longer lifespan, that may be easily installed on existing jackshaft mechanisms, that reduces risks during installation and the likelihood of failure during use, and that may be installed using commonly available tools and knowledge.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.